Reinforced insulation is required for insulation between the primary side and the secondary side of a power supply device to keep the power supply device in a safe state. Reinforced insulation is a single insulating system that provides mechanical and electrical protection on a par with double insulation against electric shocks. The double insulation referred to here is made up of basic insulation, i.e. insulation for basic protection against electric shocks, and supplementary insulation, i.e. independent insulation added to the basic insulation to ensure protection against electric shocks in the case of a defect in the basic insulation. Functional insulation, which is used to ensure proper operation of equipment, is useful for prevention of ignition and combustion. However, this insulation does not provide protection against electric shocks.
International safety standards define insulation distances needed to ensure insulation in consideration of circuit effective voltages and transient voltages. The defined insulation distances include an air clearance, that is the shortest distance between two conducting parts or between a conducting part and a conductive outer surface of equipment measured through air, and creepage distance, that is the shortest distance between two conducting parts or between a conducting part and a conductive outer surface of equipment measured along the surface of an insulator which is in between.
As described in PTL 1 for example, international standards and guidelines stipulate that the insulation distance for a welding power supply with a circuit effective voltage of 400 V should be 5.5 mm or longer in air clearance and 6.3 mm or longer in creepage distance to provide basic insulation. These standards also stipulate that insulation between an input circuit and an output circuit should constitute reinforced insulation or double insulation, and the insulation distance should be twice the basic insulation distance, i.e. an air clearance of 11 mm or longer and a creepage distance of 12.6 mm or longer.
PTL 2 discloses a method of ensuring the expandability of a battery system that includes a plurality of series-connected battery modules each having a plurality of battery cells. The battery modules have photo-couplers or other insulating devices that are used to communicate information about voltages and other measurements of the respective modules with an external management unit for the battery system. A housing for each battery module has an insulation sheet and a spatial distance between the housing and the battery cells contained inside and thereby maintains insulation from the battery cells.